In the latest Wayback Machine snapshot (27th July 2023) of the OpenAI pricing page, there's a "Simple and flexible" section that says you can "start experimenting with $5 in free credit that can be used during your first 3 months."
https://web.archive.org/web/20230727140439/openai.com/pricing
As of today (28th July 2023), that section is no longer there.
https://openai.com/pricing
The free trial is still mentioned in the help pages (e.g. https://help.openai.com/en/articles/6643435-how-do-i-get-more-tokens-or-increase-my-monthly-usage-limits ) but could they be phasing it out?